Colloquium

Upcoming Colloquium

Atomic-scale visualization of topological spin textures
Dr. Jay Gupta, The Ohio State University

September 26, 2022
11:00am in HSCI-102

Image

Spin textures in chiral magnets are of fundamental interest and may enable novel magnetic storage and computing technologies. These spin textures can have a mathematical topology ascribed to them, and our work is focused on exploring the connections between this idealization and textures in real materials. In MnGe, such textures arise from the competition of ferro-magnetic exchange, favoring aligned spins, and a so-called 'Dzyaloshinskii-Moriya interaction' (DMI) which favors perpendicular spins. In our spin-polarized STM studies of MnGe thin films, we study spin textures at the surface, where DMI may arise not only from the chiral 'B20' MnGe crystal structure, but also from the surface itself. Furthermore, the thin film structures allow us to study strain effects, and provide a path for integration into devices.

Our SP-STM images indicate helical stripe domains with a 6 nm period, which micromagnetic modeling helps us understand as a surface projection of the helical wavevector, canted away from the film normal. We can deduce the three-dimensional orientation of the helical wavevectors at domain walls, and we predict that three helical domains can meet in two distinct ways to produce either a 'target-like' or a 'π-like' topological spin texture. Both textures are observed experimentally, and are only found in slightly strained regions of the films. Topological defects in the target texture can be created, moved and annihilated with current/voltage pulsing from the STM tip. The core of the target texture itself can be similarly moved, and can also be reversibly switched with applied magnetic field.

These studies represent an initial step toward understanding the interplay of bulk and surface magnetism in chiral magnets, and the manipulation of these topological spin textures is a promising step toward future spintronics applications.

Image